Nowadays, semiconductor memories are used in every device from a main memory of a large-scale computer to a personal computer (PC), a home electric appliance, a mobile phone, and others. Memories enlarging their markets include such a NAND flash memory (a NAND Flash EEPROM) as shown in FIGS. 10A and 10B, and various kinds of memory cards (a Secure Digital [SD], multimedia card [MMC], compact flash [CF] card) or flash drives are used as media that store information such as images, moving images, sound, games, and others, storage media of a digital camera, a digital video player, an MP3 music player or the like, a mobile phone, or a mobile PC, and storage media of a digital TV and others.
If a NAND flash memory of hundreds of GB is realized, it can substitute for a hard disk drive (HDD) for a PC. As flash EEPROM nonvolatile memories, there are mainly a NOR type and a NAND type, and the NOR type has the number of times of high-speed read or read which is substantially the 13th power of 10 and is used as a command code storage for a mobile device, but it has a small effective bandwidth for write, and hence it is not suitable for file recording.
On the other hand, the NAND type can be highly integrated in comparison with the NOR type, its access time is as slow as approximately 25 μs, but burst read is possible, and this type has a high effective bandwidth. A write operation has a programming time of 200 μs to 1 ms and an erase time of approximately several ms, but the number of bits that can be programmed or erased at a time is large, and burst enables fetching write data and programming many bits at a time. Therefore, the NAND type is a memory having a high effective bandwidth, and it is widely used in the above-described markets.